Rules on intrapair and interpair correlation energy for Cl, Cl~(-) and MCI (M=H, Li, Na, K)

According to the calculation results of the intrapair and interpair correlation energy for the title systems, it has been found that the intrapair correlation energy of K shell of Cl is almost a constant and both the intrashell and intershell correlation energy of K and L shell changes little. It has also been found that in MCI series compounds the value of Cl correlation energy contribution depends on the ionicity of MCI compounds, i.e., the Cl correlation energy contribution increases with the increase of the ionic bond strength of the compound and this value is always less than the correlation energy of Cl" anion but always larger than that of Cl atom. These rules are helpful for the estimation of the correlation energy of ionic compounds and the energy changes of chemical reactions.